Actually Lincoln looked at this as a possible solution to the cultural problems of trying to integrate free blacks into white society. Considering that a civil war was being fought with that as one of the major issues, one has to accept that this was definitely a problem. However Lincoln never advocated making such exportation mandatory and his thoughts on it were purely speculative.
The war was not about freeing blacks, was not about slavery at all. It was about Northern envy of the opulence, politeness and charm it saw in such Southern cities as New Orleans, Richmond, Savannah, Charleston and Mobile. It was a war of envy, a war to increase federal power (which had it's roots in Jacksonianism) and a war to protect northern industry at the expense of Southern industy.